In distributed power vehicle systems, two or more powered vehicles are linked together and controlled in concert to pull or otherwise move one or more non-powered load vehicles. For example, in the case of a distributed power-based train, there is typically a lead locomotive followed by a number of load railcars for hauling freight, passengers, or the like, with one or more remote locomotives distributed throughout the train for helping with moving and braking the load railcars. In operation, when a throttle setting is established in the lead locomotive (e.g., by a train operator selecting a desired notch level), a distributed power control system in the lead locomotive transmits a command to the remote locomotives for complimentary control of the remote locomotives' propulsion systems. Similarly, when a braking application is applied in the lead locomotive (e.g., application of dynamic brakes or air brakes), a command is transmitted to each remote locomotive for similarly applying its respective braking system.
Certain vehicle systems utilize what is referred to as a “penalty brake” function or application. Here, upon the occurrence of a designated stimulus or based on certain operating conditions of the vehicle (e.g., the vehicle is going over a designated speed limit), a command is initiated for automatically causing the vehicle's brake system in engage to a designated extent. That is, based upon the occurrence of certain conditions, operation of the vehicle is “penalized” by automatically causing it to slow down. In the case of a distributed power train, upon application of a penalty brake function in the lead locomotive's braking system, the braking system informs the distributed power control, which subsequently communicates a braking command to the remote locomotives for engaging their braking systems. In this manner, each locomotive is braked in a similar or complementary manner, thereby maintaining an even or equal level of braking between the lead and remote locomotives, which is important for train stability and for maintaining inter-railcar force levels within designated constraints. When a penalty brake function is applied, this may result in a full brake application of the locomotive or other vehicle (meaning the vehicle's brake system is applied to the maximum extent possible for a designated time) or a limited brake application (meaning that the vehicle's brake system is applied to some extent below the maximum extent possible, e.g., 50%, for a designated time).
In a distributed power locomotive, the locomotive's braking system communicates with the distributed power control system over a serial communication line. For a penalty braking application, the braking system communicates the level of the penalty braking application (e.g., full or limited) to the distributed power control system, enabling the distributed power control system to convey this information to remote locomotives. However, if the serial communication line goes down, malfunctions, or is otherwise unavailable for reliable communications, both the braking system and the distributed power control system default to a full brake application when the penalty brake function is initiated. (In some systems, the braking system and the distributed power control system enter into what is in effect a fault mode, and self-initiate a penalty braking application at the default full level when the serial communication line goes down). This ensures that all locomotives initiate a full brake application (representing the most severe penalty, for safety purposes), even if the distributed power control system is unaware of the designated level of the penalty braking application. This in turn ensures even levels of braking at the lead and remote locomotives, but may result in the train being slowed to a greater extent than it would have been had the communication link been active, which reduces train efficiency. Additionally, initiating a full braking application stresses the train, and can be a safety hazard in and of itself, e.g., passenger injury due to quick deceleration, train derailment, or the like.